https://www.ford-trucks.com/dcforum/perf/1039.html

I posted this there, but since it may be an effect of the head design of the newer I-6's, I felt I better post this here:

An interesting side-gapping, gapping, or MSD 'oops'

After about 5000 miles on my sidegapped, and wider-than-stock-gapped Autolite plugs (5125's?) I decided to change 'em out today, and this is what I saw:

You know how the tips of plugs, or the end of a distributor rotor gets all rough after being used (sparks arcing and the transferring of electrons)? I had that effect on the side of each center electrode. But this was bad... this was on the bottom half to two-thirds of the center electrode, and was in a small area (let's say it only went ~ 1/6th or 1/7th around the total diamter of the electrode).

On top of that, the 'rough' areas never coincided linearly with the covering-electrode! On some it was at the nearly total opposite side.

So I had a good spark jumping from the base-side of the center electrode to some part of the head in each cylinder (probably the same part(?), but the way each spark plug was facing (they weren't indexed) determined where the spark jumped from the center electrode at. or that is what I'm guessing...)

The tops of the center electrodes were not rough at all. This could mean the plugs weren't firing from the tops much, or that the severe roughness that was on the side of each electrode happened during a certain changed condition (like the rare times the MSD-6A sparks would stop being multiple sparks and became single "lightening bolts" past 2500 or 3000 RPM - this is a rare condition in daily and highway driving of an 4.9 inline six).

But that is my experience for those who have MSD's and/or side gapped plugs and Inline Sixes - or whatever combination led to my strange findings.

I kept them, but do not have a camera to take a close macro picture of the effects to show you guys. Sorry.

 

[updated:LAST EDITED ON 18-Jul-02 AT 10:50 PM (EST)]That's quite informative. I never had problems when I sidegapped some plugs a year ago, but I saw no real improvement - just shorter plug life. I haven't checked my plugs since I installed my 6A two months ago (not sidegapped). I'm planning on changing them out this weekend. I'll let you know if I find similar characteristics. My six is a '79.

 

[updated:LAST EDITED ON 18-Jul-02 AT 11:22 PM (EST)]Well I'm really not too sure how informative it is.

I'm thinking it may have something to do with the heads of the later EFI 300's (I heard they have emissions considerations for air injection tubes or soemthing - something apparently sticks down in the chamber to create a hole), and it may be a high-energy ignition thing when mixed with sidegapping and wide gaps.

If you don't have a high energy ignition on your truck, I wouldn't even worry about it. I've never seen a warning of side-gapping that described the situation, so I'd bet side gapping with a normal coil pusher ignition wouldn't, or couldn't, make the spark jump that far.

There again it could have been jumping to the side of the outer area of the spark plugs, but the angle it would have to travel to do so, plus the concentrated area of firing-evidence on the center electrodes, makes me think it was going to somewhere in the combustion chamber.

If it was jumping to the side of the plugs themselves, I would expect the affected rough area on the centers to be spread out around the center electrode. Plus, and I'm not sure if this means anything, I couldn't see a corresponding 'rough' area on the side of any plug linear to the small patch on each plug's center electrode. (So this is either due to the difference in metals, or it just wasn't recieving the intended spark.)

Since so few people who have 4.9 EFI heads also add high-energy ignitions, sidegap plugs, and also (ridiculously?) widen the plug gap, I just posted this as more of a story than a warning.

here's another aside - who knows, it may even be my problem! - I hooked up another main negative battery cable a few weeks ago from the front, driver's side of the HEAD(!) to the negative post on my battery. My starter cranking speed increased, and other goals were to better the engine ground for the ignition, and to better the ground for the charging system. Of course this could lead to specualtions galore, but the theory behind the idea is a solid one, so grounding what should, and is, grounded elsewhere should not increase the likelihood that the spark would jump past the sparkplug electrode and over to the head. But of course maybe it is doing just that!?

I like my head-grounding idea for all the theoretical reasons it should work well, so I'm going to hold on to it for awhile - like three weeks, then check a few plugs (now non-sidegapped, gapped at .050 instead of the stock .044). Feel free to post warnings and conjectures about it though - it's not like it's a common practice, so I could be off my rocker.

I have to admit I can't remember if the ends of the center electrodes on plugs get the rough surfaces I have seen on rotors, or on the sides of my plugs, but if they do, then there is no indication of roughness on the ends, so apparently it may never (even before the added neagtive battery cable) have been firing the right direction?

So there's the WHOLE story, guys...
disect it as you will.